1. Field of the Invention
The present invention relates to a wavelength converting device suitable for a blue light source device or the like.
2. Related Art Statement
A second harmonic wave generating device with reduced optical damage and without the necessity of quasi-phase matching and a high precision control of domains was proposed in Japanese patent publication 8-339, 002A. According to the publication, it is produced a substrate of a single crystal of potassium lithium niobate or potassium lithium niobate partially substituted with tantalum is produced by a micro pull-down method, and an optical waveguide made of the same kind of material as the substrate is produced on the substrate.
Further, potassium lithium niobate having an absorption coefficient of 0.3 cm−1 or lower in a wavelength range of blue to green light is known (Japanese Patent publication 8-333199 A: Proceeding of International Symposium on Laser and Nonlinear Optical Materials, 1997, T8.4, M. Adachi et al).
Japanese patent publication 2002-250, 949A further discloses that it is known to adhere a substrate to be processed made of a non-linear optical crystal onto a supporting body and the substrate is then mechanically processed to form an optical waveguide. According to the publication, a substrate made of lithium niobate single crystal is used to form an optical waveguide.
When it was tried to irradiate blue light from a second harmonic wave generating device using potassium lithium niobate crystal, however, the output power of the blue light fluctuated when the input power of a fundamental wave is elevated to a value of 1 W or larger. That is, the irradiated blue light was observed to prove that irregular cycles each including periods of increase and decrease of the light intensity were repeated on a non-periodic basis.
Further, also in the second harmonic wave generating device using lithium niobate single crystal, it was found that irregular cycles each including periods of increase and decrease of the light intensity were repeatedly observed, when the power of fundamental wave oscillated from a light source is 500 mW or larger.